In-situ twin-electrode spectrocyclic voltammetry with a cell composed of a pair of Nafion®-coated indium tin oxide electrodes each incorporating Ru(bpy)₃²⁺ and methylviologen

Electrochemical redox reactions in a twin-electrode (TE) type cell composed of a couple of Nafions®-coated indium tin oxide (ITO) electrodes each incorporating Ru(bpy)₃²⁺ and methylviologen (MV²⁺) were analyzed by in-situ spectrocyclic voltammetry. The cell system, ITO/Nafion®[Ru(bpy)₃²⁺]/aqueous electrolyte/Nafion[MV²⁺]/ITO, showed changes in visible absorption spectra induced by cyclic scanning of the potential difference between the two ITO electrodes. The spectral changes were attributed to the redox reactions of Ru(bpy)₃^3+/2+ and MV^2+/+· showing a multicolor electrochromism. The potential difference (+ 1.73 V) of the major redox wave in the cyclic voltammogram (CV) of the TE cell were close to the values (+ 1.76 V) calculated from the redox potentials of each species. Small peaks in the TE-CV suggested side reactions with H₂O and O₂, as well as migrations of the redox compounds into the opposite membranes. When each redox membrane was precycled repeatedly in an aqueous electrolyte solution, before fabricating a TE cell, the cell showed very stable behavior after repeated cyclic scanning. It has been shown that the present in-situ TE spectrocyclic voltammetry is useful for studying reactions occurring in practical devices.